The present invention relates to lasers and especially to lasers having a specially formulated coolant having fluorescent dyes therein and the method and apparatus for replacing decomposed dye.
In the past, it has been suggested that the efficiency of a neodymium (Nd) glass laser pumped by a xenon flashlamp can be improved by the circulation of fluorescent dyes between the laser rod and the flashlamp. The fluorescent dyes were used to absorb in the spectral region in which the Nd ions do not absorb and to fluoresce strongly at one of the pump bands of the laser rod. Prior art tests in this area have indicated a more efficient utilization of the flashlamp output. The use of a dye solution in place of the normal flashlamp/laser rod coolant results in an improvement in the efficiency of the overall electrical to laser output. This improved energy conversion can be used to maintain the existing energy input to the flashlamp if higher laser output is needed or to reduce the energy to the flashlamp so as to have the same laser output with a lower demand for electrical energy. The reduction and input power reduces the heat loading on the system and can markedly extend the useful life of the flashlamp.
A mixture of ethylene glycol and water is normally used as a coolant in a neodymium yttrium aluminum garnet, or Nd:YAG, laser system. The coolant has been proven adequate for the thermal load of the laser system and it functions not only as a heat exchanger, but also as a transparent optical medium of matchiing refractive index between the flashlamp, silver reflector and laser rod. The coolant as currently designed will not enhance flashlamp output by itself, and in fact, contamination of the coolant by inorganic or organic molecules can reduce laser output by absorbing visible flashlamp output energy in the Nd:YAG absorption band. The absorption spectrum of Nd:YAG is only a small fraction, or approximately eight percent (8%), of the input energy to the lamp and is absorbed by the laser rod. The remaining energy is wasted as heat and is removed by the coolant from the pumping cavity to the heat exchanger. The coolants used in the Nd:YAG lasers have a number of problems which the current invention is directed at improving.
Coolant acidification due to ultraviolet light from the flashlamp results in chemical corrosion of oxidizable metals such as brass, nickel, stainless steel and aluminum. In addition, coolant coloration will absorb some of the main Nd:YAG pump bands from the flashlamp to the rod reducing the laser output. Finally, flocculent turbidity coats the rod, lamp and reflectors and causes the light scattering which reduces the laser output and requires frequent costly maintenance.
The prior art used of fluorescent dyes is discussed in the journal of Quantum Electronics, Volume QE9, No. 1, January, 1973, starting on page 43, entitled "Improving the Pumping Efficiency of Nd.sup.3 Glass Laser Using Dyes". The following U.S. Pat. Nos. are also cited as of interest: 3,079,347 to C. G. B. Garrett, et al.: 3,174,938 to R. R. Soden, et al.; 3,417,345 to A. Y. Cabezas, et al.; 3,729,690 to E. Snitzer; 3,813,613 to H. G. Danielmeyer, et al.; 3,999,145 to J. J. Gilman, et al.; 4,081,761 to N. T. Melamed, et al.; and 4,163,199 to C. E. Treanor.